Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Also, Functional Electrical Stimulation (FES) systems such as the Freehand system by NeuroControl (Cleveland, Ohio) have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Each of these implantable neurostimulation systems typically includes one or more neurostimulation leads implanted at the desired stimulation site and an implantable neurostimulator, such as an implantable pulse generator (IPG), implanted remotely from the stimulation site, but coupled either directly to the leads or indirectly to the leads via one or more lead extensions in cases where the length of the leads is insufficient to reach the IPG. Thus, electrical pulses can be delivered from the neurostimulator to the leads to stimulate the tissue and provide the desired efficacious therapy to the patient.
In the context of an SCS procedure, one or more neurostimulation leads are introduced through the patient's back into the epidural space, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array. One type of commercially available neurostimulation lead is a percutaneous lead, which comprises a cylindrical body with ring electrodes, and can be introduced into contact with the affected spinal tissue through a Touhy-like needle, which passes through the skin, between the desired vertebrae, and into the epidural space above the dura layer. For unilateral pain, a percutaneous lead is placed on the corresponding lateral side of the spinal cord. For bilateral pain, a percutaneous lead is placed down the midline of the spinal cord, or two or more percutaneous leads are placed down the respective sides of the midline of the spinal cord, and if a third lead is used, down the midline of the special cord. After proper placement of the neurostimulation leads at the target area of the spinal cord, the leads are anchored in place at an exit site to prevent movement of the leads. To facilitate the location of the neurostimulator away from the exit point of the leads, lead extensions are sometimes used.
Whether or not lead extensions are used, the proximal ends of the neurostimulation leads exiting the spinal column are passed through a tunnel subcutaneously formed along the torso of the patient to a subcutaneous pocket (typically made in the patient's abdominal or buttock area) where a neurostimulator is implanted. The subcutaneous tunnel can be formed using a tunneling tool over which a tunneling straw may be threaded. The tunneling tool can be removed, the leads threaded through the tunneling straw, and then the tunneling straw removed from the tunnel while maintaining the leads in place within the tunnel.
The neurostimulation leads are then connected directly to the neurostimulator by inserting the proximal ends of the stimulation leads within one or more connector ports of the IPG or connected to lead extensions, which are then inserted into the connector ports of the IPG. The IPG can then be operated to generate electrical pulses that are delivered, through the electrodes, to the targeted tissue, and in particular, the dorsal column and dorsal root fibers within the spinal cord.
The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. Intra-operatively (i.e., during the surgical procedure), the neurostimulator may be operated to test the effect of stimulation and adjust the parameters of the stimulation (e.g., the electrodes that are acting as anodes or cathodes, as well as the amplitude, duration, and rate of the stimulation pulses). The patient may provide verbal feedback regarding the presence of paresthesia over the pain area, and based on this feedback, the lead positions may be adjusted and re-anchored if necessary. A computerized programming system, such as Bionic Navigator®, available from Boston Scientific Neuromodulation Corporation, can be used to facilitate selection of the stimulation parameters. Any incisions are then closed to fully implant the system. Post-operatively (i.e., after the surgical procedure has been completed), a clinician can adjust the stimulation parameters using the computerized programming system to re-optimize the therapy.
The efficacy of SCS is related to the ability to stimulate the spinal cord tissue corresponding to evoked paresthesia in the region of the body where the patient experiences pain. Thus, the working clinical paradigm is that achievement of an effective result from SCS depends on the neurostimulation lead or leads being placed in a location (both longitudinal and lateral) relative to the spinal tissue such that the electrical stimulation will induce paresthesia located in approximately the same place in the patient's body as the pain (i.e., the target of treatment). If a lead is not correctly positioned relative to the tissue or relative to another lead, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy.
Multi-lead configurations have been increasingly used in electrical stimulation applications (e.g., neurostimulation, cardiac resynchronization therapy, etc.). In the neurostimulation application of SCS, the use of multiple leads that are grouped together in close proximity to each other at one general region of the patient (e.g., side-by-side parallel leads along the spinal cord of the patient), increases the stimulation area and penetration depth (therefore coverage), as well as enables more combinations of anodic and cathodic electrodes for stimulation, such as transverse multipolar (bipolar, tripolar, or quadra-polar) stimulation, in addition to any longitudinal single lead configuration. In more advanced applications, multiple leads may be placed in different locations of the patient. For example, in an SCS application, one lead may be placed along the cervical region of the spinal cord, and another lead may be placed along the lumbar region of the spinal cord. As another example, in a combined SCS/PNS application, one lead may be placed along the spinal cord of the patient, and another lead may be placed in a peripheral location of a patient (e.g., an arm or a leg).
Whether the multiple leads are implanted in the patient in close proximity to each other at a particular location or implanted in the patient at separate locations, selection of cathodes/anodes requires the identification of the electrodes that are positioned close to each other and knowledge of the relative positions of the electrodes that are to be activated as the cathodes or anodes. Conventional electrical field-based techniques, such as those described in U.S. Pat. No. 6,993,384, entitled “Apparatus and Method for Determining the Relative Position and Orientation of Neurostimulation Leads,” and U.S. patent application Ser. No. 12/623,976, entitled “Method and Apparatus for Determining Relative Positioning Between Neurostimulation Leads” (now U.S. Pat. No. 8,380,301), which are expressly incorporated herein by reference, have been developed to estimate the positions of the electrodes relative to each other by determining longitudinal offset and/or transverse separation between the leads. These techniques usually assume that the electrodes are arranged in-line along each lead and the arrangement of the electrode array is known so that certain patterns of the induced electrical field can be examined.
If not already taken into account by the programming system, information related to the arrangement of electrode arrays may be obtained through user input if it is available (e.g., a user can enter the spatial orientation of the leads and/or electrodes obtained from a recent radiographic image into the programming system). However, radiographic imaging may not always be available, and even when it is, the images do not allow for identification of each electrode in the array unless certain prior information is available, e.g., lead type, lead-port mapping and electrode configuration. If such prior information is limited, identifying the electrode arrays may be difficult. This problem may be more complicated when, for example, different types of extensions (e.g., splitters) are used to connect the leads to the neurostimulator, which may result in an electrode array configuration that is different from the physical electrode array arrangement. Furthermore, lead position determination software installed in current neurostimulation systems oftentimes need to be updated to accommodate new or unknown lead designs.
There, thus, remains a need for an improved generic technique for identifying electrodes that are in proximity to each other, the relative positioning between the electrodes, and the configuration of the electrodes.